Since the end of the 20th century the cellular telephone industry has had enormous development in the world. From the initial analog systems, such as those defined by the standards AMPS (Advanced Mobile Phone System) and NMT (Nordic Mobile Telephone), the development has during recent years been almost exclusively focused on standards for digital solutions for cellular radio network systems, such as D-AMPS (e.g., as specified in EIA/TIA-IS-54-B and IS-136) and GSM (Global System for Mobile Communications). Different digital transmission schemes are used in different systems, e.g. time division multiple access (TDMA) or code division multiple access (CDMA). Currently, the cellular technology is entering the so called 3rd generation, providing several advantages over the former, 2nd generation, digital systems referred to above. Among those advantages an increased bandwidth will be provided, allowing effective communication of more complex data. The 3rd generation of mobile systems have been referred to as the UMTS (Universal Mobile Telephony System) in Europe and CDMA2000 in the USA, and is already implemented in Japan to some extent. Furthermore, it is widely believed that the first generation of Personal Communication Networks (PCNs), employing low cost, pocket-sized, cordless telephones that can be carried comfortably and used to make or receive calls in the home, office, street, car, etc., will be provided by, for example, cellular carriers using the next generation digital cellular system infrastructure.
Accompanying the increase in use of portable communication terminals has been a desire for easy and convenient operation of these devices. In particular, manufacturers of mobile cellular radio telephones have long sought to provide efficient hands-free operation. In automobiles, for example, it is desirable to provide hands-free telephones for driver safety and convenience. With hands-free operation, the driver of a vehicle may use both hands to control the automobile.
One method of hands-free operation can be achieved by simply increasing the gain of the telephone's microphone and speaker to allow a user to speak and listen from some distance from the unit. Such a telephone is commonly referred to as a speakerphone. However, several problems are associated with a system constructed in this manner. For example, feedback and interference from ambient noise often make it difficult to clearly understand the words of the user. To help offset problems due to ambient noise, the microphone gain can be reduced by placing an external microphone connected via a wire to the main body of the radiotelephone close to the user's mouth. Nevertheless, the telephone speaker must still operate at high volume thereby diminishing the privacy of the received call.
Another solution is a headset with a microphone and a speaker, wherein a cable connects the headset to the main telephone apparatus. Although having improved performance and privacy, the headset must still be wired to the radiotelephone unit. Wire connections are often inconvenient, particularly for use with a portable radiotelephone.
For this reason, cordless headsets, communicating wirelessly with communication terminals, have been developed. In cordless headset systems of today, communication may be achieved e.g. by infrared radiation or radio transmission. Headsets have also been disclosed including bluetooth technology for short-range radio communication with a communication terminal, such as a mobile phone.
In order to operate the cordless or wireless headset, a power supply unit is needed. Since no cable is used, the power supply unit has to be contained in the headset, normally in the embodiment of a battery, which also means that the battery must be carried by the user when the headset is used. Consequently, portable cordless devices in general, and cordless headsets in particular, have strong and somewhat conflicting market requirements: They should be as small and light-weight as possible, and the battery should last for as long as possible. However, the skilled person realises that longer-lasting batteries are larger and/or heavier than shorter-lasting batteries, and the manufacturers will always strive to make their products smaller and smaller to attract more consumers. Obviously, the manufacturer that finds a solution to how to combine the smallest product with the highest battery time will have a huge competitive advantage, although most likely there always will be a compromise to some extent between size/weight and battery time.
One attempt to overcome the drawbacks of conventional headset solutions is disclosed in U.S. Pat. No. 5,590,417 to Rydbeck, incorporated herein by reference, which suggests wireless means for communicating between a headset and a portable radio telephone unit. Further, the headset operates in two modes. According to a first mode, the headset may be mounted on the radio telephone where it serves as a speaker and microphone. Also, the headset can be separated from the body of the radiotelephone and placed on the head of the user. In this mode of operation, the headset receives and transmits communication signals from and to the body of the radiotelephone during a call, thus providing hands-free operation. When mounted on the radio telephone a battery in the headset may be charged from the radio telephone. A drawback of this solution is that the headset needs to be stored attached to the phone. One of the basic ideas with cordless headsets is that the communication terminal, such as a mobile phone, may be kept in e.g. a bag or a pocket, whereas the headset is stored somewhere else where it is easily reached when needed.
Consequently, there is still a need for improvements in the art of cordless headsets, satisfying the market demands on dimensions, battery time and ease of use.